The overall objectives of this ongoing investigation are elucidation of fundamental biological mechanisms regulating the formation, transfer, replication and genetic expression of R factors --- and modification of these processes as a result of information gained about their control. Objectives set during the current year include: continued study of physical and functional relationships between different R factors and between R factors and other plasmids by the electron microscope heteroduplex technique, 2) investigation of biological functions of plasmids constructed in vitro from fragments of other genomes and inserted into E. coli by transformation; 3) study of the genetic expression of specific R factor DNA species using the plasmid transformation techniques developed in this laboratory.